Recovery of Alkali from Bayer Red Mud Using CaO and/or MgO

Bingxin Zhou,Fangfang Chen,Fangfang Zhang,Shaotao Cao,Yi Zhang

doi:10.3390/min9050269

Abstract

Recovering alkali from Bayer red mud is crucial for storage security, resource utilization and environmental protection. In this study, the addition of MgO and/or CaO was conducted to recover alkali from red mud with a hydrothermal method for the first time. A synergistic result with a residual Na2O/SiO2 weight ratio of 0.03 was obtained by adding the blend of CaO and MgO at an appropriate temperature. MgO was found to be more temperature-dependent than CaO when substituting Na2O from red mud due to their different hydration processes. The alkali recovery was controlled by a reaction at a temperature of <200 °C and by internal diffusion at a higher temperature for MgO, but controlled by internal diffusion for CaO in the whole temperature range studied. The formation of hydrotalcite-like compounds with a loose structure was verified with the help of XRD, FTIR, and SEM-EDS. It was proved that both the reaction kinetics and the characteristics of solid products have a significant influence on the recovery of alkali.

Highlights

IntroductionChina produced 69.02 million tons of alumina in 2017, with more than 100 million tons of red mud generated [1]
Red mud is the solid waste emitted from the aluminum industry
Several processes have been proposed to neutralize the alkali in red mud, such as acids and acid gases neutralization, seawater neutralization, microbial neutralization and revegetation [4,8,11,12,13,14,15], among which seawater neutralization has been highly valued for the abundance and low cost of seawater

Summary

Introduction

China produced 69.02 million tons of alumina in 2017, with more than 100 million tons of red mud generated [1]. In the seawater neutralization process, the Ca- and Mg-rich brines play an important role in the reduction of pH and in the precipitation of hydroxide, carbonate or hydroxycarbonate minerals [13,16,17]. This method is only suitable for coastal areas

Methods

Results

Conclusion